A ball valve is a valve that opens and closes by rotation of a ball. The ball has a port therethrough such that when the port is in line with ends of the valve, flow will occur. The ball sits in, and is sealed by, valve seats.
As is well known, a main requirement in the manufacture of ball valves is that an effective seal be maintained between the valve seats and the ball at all times. Many and varied forms of annular seats have been devised for this purpose.
One ball valve seat arrangement is described in U.S. Pat. No. 3,384,341 to Ripert (“Ripert”). A main feature of that invention resides in the cross-sectional shape of the seats (or sealing rings) that is formed to have a somewhat arcuate overall formation with a substantially concave outer surface and a substantially convex inner surface. When pressure is applied to the inner surface, by contact with the ball, it tends to flex inwardly and due to the concavity of the outer surface, the middle portion of the ring increases in circumference under tension. By way of background, the valve of Ripert will be described in further detail with reference to FIGS. 1 to 3 herein. With particular reference to FIG. 1 of Ripert, a portion of a typical ball valve construction is shown as consisting of a two piece valve body 10, having a main portion 12 including a tapped bonnet portion 14 receiving a valve spindle 16. The main body 10 is recessed axially to provide a fluid inlet 18 and an enlargement 20 constituting a valve chamber 21. The outer end of the enlargement 20 is tapped to threadably receive the minor portion of the valve body 22, which is also recessed axially to provide a fluid inlet 24. The inner ends of the fluid inlets 18 and 24 are each provided with sealing ring accommodating grooves 30 into which is adapted to fit sealing ring 32. The terminal end 17 of the spindle 16 is shaped in rectangular form to fit loosely with a corresponding slot 33 and a ball 34. Rotation of the spindle 16 causes a corresponding rotation of the ball 34, which includes an axial recess 35, between open and closed positions relative to the fluid inlets 18 and 24 with the sealing rings 32 acting to maintain the seal between the outer spherical surface of the ball and opposed portions of the valve body surrounding the fluid passages. FIG. 2 shows a sealing ring in perspective and partially broken view of Ripert, in which concave outer surface 50 and convex surface 52 are identified. In operation, and assuming that the spacing between the opposed ring accommodating grooves 30 is such that a minimum deflection only of the sealing rings 32 as shown in FIG. 3 is necessary, the outer surface of the ball 34 (FIG. 1) bears against the apex 57 of the inner surface of the ring so that it is urged inwardly along the centre as indicated by the arrow A. The deflection of the ring 32 in the direction A, due to the concave outer surface 50, places the ring under tension causing it to bear against the ring accommodating groove 30 along the direction of the arrows B and C bringing the surfaces 51 and 54 more tightly against the groove surfaces 61 and 63. At the same time, a convex inner surface is altered, as indicated at D, conforming to the curvature of the ball 34. The preferred minimum deflection illustrated in FIG. 3 will give the desired maximum sealing effect with the minimum of friction contact with the ball 34 making for ease in valve adjustment but the same maximum sealing effect is obtained with a condition of maximum deflection of the sealing ring, as shown in FIG. 3, without seriously affecting the friction resistance by the contact of the sealing rings with the ball 34. In effect, any deflection of the sealing rings by the ball outer surface bearing on the inner surface 51 of the ring increases the circumference while placing the ring under tension giving the desired sealing effect in the directions B and C. In other words, when the ball 34 abuts the convex surface 52, it will stretch or expand the circumference of the convex surface 52 thus placing it under tension. The spacing of the concave surface 50 from the connecting surface or inclined surface wall 65 of the groove 30 allows the ring to be placed under tension on bearing of the surface 52 by the ball 34. The sealing ring may also be in an alternative form by having a smooth arcuated inner surface rather than a surface with an apex. The same principles of deflection apply.
In the ball valve seat arrangement of Ripert, pressure rises in the valve chamber 21 (or valve cavity). Also, in Ripert there is a space between the concave surface 50 and the wall 65 of the groove 30 and pressure also rises in this space. Such pressure rise in these areas is not desirable. It would therefore be desirable to have a ball valve seat arrangement where relief of the cavity pressure, or pressure in the aforementioned space, could be achieved. Although the ball valve seat arrangement of Ripert has been discussed above, relief of cavity pressures in ball valve seat arrangements of different forms would also be desirable.